The emitting color of the Organic Light-Emitting Diode (OLED) depends upon organic emitting materials, or organic light-emitting dyes on the substrate mixed with the required light color. Referring to FIG. 1, an OLED 100 of related art comprises a substrate 110, an anode 120, a hole transport layer 140, an organic light-emitting layer 150, an electron transport layer 170 and a cathode 190. When a forward bias voltage is charged on this structure, an electric hole 141 and electron 171 will be separately injected from the cathode and anode into a hole transport layer 140 and Electron transport layer 170, and then transmitted to the organic light-emitting layer 150, where they are overlapped for emitting light.
An OLED is typically categorized into micro-molecular and high-molecular OLED according to the types of substrate made of organic light emitting materials.
Micro-molecular substrate OLED is generally fabricated byway of vacuum evaporation, such that micro-molecular materials have a better film forming quality. However, the corresponding manufacturing equipment is limited to applications on small-sized panels due to a higher investment costs. Conversely, high-molecular substrate OLED is fabricated through a solution manufacturing process, which combines a coating or ink-jet method without needing large-size vacuum devices. Thus, the manufacturing process is significantly simplified with lower investment costs. In addition, highly attractive large-size displays or lighting devices are able to be developed thanks to smaller dimensions of substrate and few limitations on screen printing or ink-jet printing.
The light-emitting layer of a white-light OLED is divided into single-layer and multi-layer.
For multi-layer white-light OLED, the carrier's overlapping area will displace with the change of voltage, and lead to the deviation of light color, owing to the fact that the transfer rate of electron and electric hole differs from each other in different layers, and also varies with the changing voltage.
For single-layer white-light OLED, the white emitting layer is formed by a vacuum evaporation method, whereby micro-molecular orange and blue dyes, or red, green and blue dyes are mixed synchronously into micro-molecular substrate materials. Due to a smaller portion of dyes mixed into white-light OLED in relation to micro-molecular substrate materials, it makes it difficult to jointly control the evaporation percentage, and the components of dyes are easy to change, thus resulting in poor color rendering and lower performance. While generating white color of high color rendering with three wavelengths or more, it becomes more difficult to synchronously control three or above dye molecules in addition to substrate materials, leading to poorer color rendering and performance in the applications.
Alternatively, the white emitting layer of the single-layer white-light OLED is formed by mixing red, green and blue dyes into high-molecular substrate materials via a solution manufacturing process. Nonetheless, it has poorer brightness and emitting efficiency and a shorter lifecycle than micro-molecule. In addition, a lower level of color reliability and purity will encounter difficulty in the application of a white-color OLED.